1. Field of the Invention
The present invention relates to a pressure detecting apparatus having a pressure introducing pipe installed on pipe members for intake and exhaust systems of internal combustion engines such as an intake surge tank and an exhaust pipe for detecting pressure in the intake and exhaust systems and an installation structure of the same on the pipe members
2. Description of Related Art
A conventional installation structure of a pressure detecting apparatus J1 is shown in FIGS. 23A and 23B. In internal combustion engines for vehicles, a detection of inner pressure in an intake surge tank (pipe member) 100 of an engine EN becomes necessary mainly for fuel injection control. Therefore, as shown in FIG. 23A, the pressure detecting apparatus J1 is installed on the intake surge tank 100 with an airtight connection therewith. A throttle body 101, an intake duct 102, an air cleaner 103 and the intake surge tank 100 constitute the intake system.
FIG. 23B shows a schematic cross sectional view of the pressure detecting apparatus J1 installed on the intake surge tank 100. The pressure detecting apparatus J1 is provided with a pressure chamber 11, on inner wall of which a pressure detecting element 10 is mounted. The pressure chamber 11 is communicated with an inner space 100a of the intake surge tank 100 through a passage 12a of a pressure introducing pipe 12. A sealing member 13 such as an O ring is provided for securing an airtight connection of the pressure detecting apparatus J1 with the intake surge tank 100.
The pressure detecting apparatus J1 is fixed to the intake surge tank 100 by screws or adhesives. With the structure mentioned above, the pressure in the intake surge tank 100 is introduced from the passage 12a of the pressure introducing pipe 12 to the pressure chamber 11 and detected by the detecting element 10.
A blow-by gas introducing pipe 104 is generally connected to the intake surge tank 100 for internal combustion engines. This is not for releasing to an atmosphere the blow-by gas escaped to a crank room through a gap between a cylinder liner and a piston ring, when fuel mixture is burned in a combustion chamber, but for returning the same to the intake system for combustion. As shown in FIG. 24A illustrating a partly exploded inside view of the intake surge tank 100, the blow-by gas introducing pipe 104 is communicated with inside of the intake surge tank 100. The blow-by gas includes a plenty of emission 105 containing dirty material such as moisture and oil.
The dirty material not only floats at a gaseous state in the inside of the intake surge tank 100 but also adheres at a liquid state to inner walls of the intake surge tank 100. That is, the inside of the intake surge tank 100 is filled with dirty material.
In an EGR system in which a part of exhaust gas is mixed with fuel mixture to reduce a combustion temperature in the combustion chamber so that formation of NOx, nitrogen oxide, may be limited, an EGR introducing pipe is also connected to the intake surge tank 100 for returning the part of exhaust gas to the intake surge tank 100. Dirty material also floats and adheres to the inside of the intake surge tank 100, similarly as is done by the blow-by gas introducing pipe.
An opening and closing movement of an intake valve according to an operation of the internal combustion engine causes intake air to flow and to interrupt to flow so that aerial vibration or pressure variation in a short period of cycle, that is, a pressure pulsation, may occur in the intake surge tank 100 (intake pipe). As shown in FIG. 24B, which shows a measurement result of the inner pressure of the intake surge tank 100 when a vehicle runs at a speed of 90 km/h, the pressure pulsation in a 15 ms cycle and with 6.7 kPa amplitude (fluctuation of pressure) can be observed.
The pressure detecting apparatus J1 has the airtight connection with the intake surge tank 100, as shown in FIG. 24B. When the pressure pulsation in the intake surge tank 100 occurs and the pressure is changed from a low point 110 to a high point 111, as shown in FIG. 24B, an air flow K1 toward the pressure chamber 11 from the inside space 100a through the passage 12a takes place instantaneously, as shown in FIG. 24C.
This is due to a reason that, even if the pressure is changed instantaneously from the low point 110 to the high point 111 and the entire pressure in the inside space 100a of the intake surge tank 100 becomes high, there exists a time delay before inner pressure of the pressure chamber 11 becomes high and low pressure is kept in the pressure chamber 11 for a very short period of time, since the passage 12a between the pressure chamber 11 and the intake surge tank 100 is narrow. Therefore, the air flow K1 takes place from the inside space 10a of the intake surge tank 100 with high pressure to the pressure chamber 11 with low pressure.
Then, after the pressure in the pressure chamber 11 has become high, when the pressure of the inside space 100a of the intake surge tank 100 is changed to a point 112, as shown in FIG. 24B, on the contrary to the above mentioned phenomenon, an air flow K2 toward the inside space 100a from the pressure chamber 11 through the passage 12a takes place, as shown in FIG. 24C. Gas is exchanged between the inside space 100a and the pressure chamber 11 by the air flow K1 and K2 which alternately take place.
The gaseous dirty material 105 and the liquid dirty material 106 in the inside space 100a of the intake surge tank 100 passing through the passage 12a of the pressure introducing pipe 12 adhere to and accumulate on inner walls of the passage 12a and the pressure chamber 11. When liquid material having a high viscosity such as oil are adhered to a surface of the detecting element 10, responsiveness of the detecting element 10 becomes slow so that an accurate pressure may not be detected.
To cope with the invasion of the dirty material, there have been proposed various methods that a pressure detecting device is communicated with a bypass passage provided so as to flow intake air from other than a throttle valve main passage or the pressure detecting device is communicated with a bypass passage provided so as to flow intake air for idling combustion, as shown in JP-A-63-229341, JP-A-2-124440, JP-A-3-277935, JP-A-6-129935 and JP-A-6-137984. 
However, in the methods mentioned above, not only a complicated passage has to be provided, but also fuel mixture ratio has to be controlled in consideration of an air flow volume in the bypass passage which is variable according to the inner pressure of the intake surge tank. Further,when dirty material is accumulated in the bypass passage to an extent that the air flow volume therein is reduced, the fuel mixture ratio control becomes more complicated. As the case may be, the air flow volume in the bypass passage has to be detected separately by an air flow detecting device.
Furthermore, as shown in JP-A-63-295940, there is proposed a method that liquid material (water in this case) entered into the pressurized passage is vaporized and eliminated by electric heating. According to this method, a device for controlling the electric heating and a circuit thereof have to be equipped in the pressure detecting device for the intake pipe, resulting in a complicated construction and higher cost.
Moreover, as shown in JP-U-57-138037 and JP-U-62-35244, there is a method that invaded dirty material is accumulated in a room provided separately before entering into the pressure detecting device. However, the accumulating capacity of the room has a predetermined upper limit and, if the accumulated volume of the invaded dirty material exceeds the limit, the dirty material enters into the pressure detecting device.
The various problems mentioned above such as the necessity of the complicated passages and the device and circuit separately provided for air flow control are also applicable to an exhaust gas pressure detecting device installed on pipe members of the exhaust gas systems for internal combustion engines.
An object of the present invention is to provide a first installation structure of a pressure detecting apparatus on an intake and exhaust system, according to which dirty material contained in the gas (intake air or exhaust gas) flowing in the intake and exhaust gas system are unlikely to enter into the pressure detecting apparatus.
To achieve the object, in the structure of installing the pressure detecting apparatus on a pipe member for an intake and exhaust system of an internal combustion engine in which gas flows according to an operation of the internal combustion engine, a pressure introducing pipe having a pressure inlet and a pressure outlet is connected on a side of the pressure inlet to the pipe member and on a side of the pressure outlet to the pressure detecting device so that inner pressure in the pipe member may be introduced to and detected by the pressure detecting apparatus, a throttle passage having a throttle is disposed in the pipe member along a flow direction of the gas for increasing a flow speed of the gas and the pressure inlet is positioned in a vicinity of the throttle.
With a compact structure with the throttle as mentioned above, the throttle causes to increase the flow speed of the gas just before the pressure inlet in order for the dirty material contained in the gas not to be stagnant. As a result, the invasion of the dirty material into and the adhesion of the same to the pressure detecting apparatus may be limited.
It is preferable that the pressure inlet is positioned on a down stream side of the gas flow with respect to the throttle, more preferably, 3 to 50 mm far away from the throttle in the flow direction of the gas in view of the compact structure effective for preventing the dirty material due to the increased gas flow speed.
To achieve effectively the increased gas flow speed, a gas flow cross sectional area of an exit of the throttle passage is, preferably, larger than that of the throttle but smaller than that of the entrance of the throttle passage. In more details, a ratio of the gas flow cross sectional areas of the throttle, the exit and the entrance falls within a range from 1:5:10 to 1:50:70. Further, it is preferable that a length of the throttle passage from the entrance to the exit is 10 mm to 100 mm and an inner diameter of the throttle is 1 mm to 10 mm.
If the pressure introducing pipe has a projecting portion protruding from an inner wall of the throttle passage into an inside of the throttle passage to position the pressure inlet into the inside of the throttle passage, the dirty material transferred along the inner wall of the throttle passage is unlikely to be entered into the pressure inlet.
Preferably, a length of the projecting portion is 3 mm to 15 mm and a gap between the pressure inlet and the throttle in a protruding direction of the pressure introducing pipe into the throttle passage is 1 mm to 5 mm. The pressure inlet is, preferably, opened toward a downstream of the gas flow for more effectively limiting the invasion of the dirty material into the pressure detecting apparatus.
It is another aspect of the present invention to provide a second structure of installing a pressure detecting apparatus on a pipe member for an intake and exhaust system of an internal combustion engine in which gas flows according to an operation of the internal combustion engine. The second structure is provided with a pressure introducing pipe having a pressure inlet and a pressure outlet, which is connected on a side of the pressure inlet to the pipe member and on a side of the pressure outlet to the pressure detecting apparatus so that inner pressure in the pipe member may be introduced to and detected by the pressure detecting apparatus. The pressure introducing pipe has a projecting portion partly protruding into an inside of the pipe member to open the pressure inlet toward a downstream of the gas flow and the projecting portion on an upstream side of the gas flow is provided with a tapered portion inclined by a predetermined angle with respect to an protruding direction of the pressure introducing pipe into the pipe member.
The pipe member may be provided with a throttle passage. In this case, the projecting portion of the pressure introducing pipe may protrude into an inside of the throttle passage.
With he second structure mentioned above, the projecting portion of the pressure introducing pipe may smoothly repel the gas flow due to the tapered portion inclined by a predetermined angle. Further, as the pressure inlet is opened toward a downstream of the gas flow, in addition to the tapered portion, the invasion of the gas flow into the pressure inlet may be effectively limited. The predetermined angle is, preferably, 10 to 70 degrees angle.
To make the gas flow more smoothly repel, it is preferred that the projecting portion on an upstream side of the gas flow is shaped convex to constitute an acute angle portion having 10 to 70 degrees in a cross section thereof perpendicular to the protruding direction of the pressure introducing pipe into the pipe member or the throttle passage.
A cross section of the projecting portion perpendicular to the protruding direction of the pressure introducing pipe into the pipe member or the throttle passage may be formed in a shape of an ellipse having a long axis in a flow direction of the gas to expel much more smoothly the gas flow. Preferably, the ellipse is a streamlined shape whose area is narrower on a downstream side of the gas flow.
It is preferred that a gas flow area at an opening portion of the pressure inlet is not larger than that at any other portion of the pressure introducing pipe. That is, the gas flow area at an opening portion of the pressure inlet may be equal to or ⅘ to {fraction (1/10)} of the gas flow cross sectional area of the pressure introducing pipe.
A filter element having ventilating holes for preventing dirty material may be provided inside the pressure introducing pipe between the inlet and the outlet.
If a blow-by gas introducing pipe or an EGR introducing pipe is connected to the pipe member, it is preferable that the pressure introducing pipe is connected to the pipe member on a downstream side of the gas flow with respect to the blow-by gas introducing pipe or the EGR introducing pipe.
It is a further aspect of the present invention to provide a third installation structure of installing a pressure detecting apparatus on a pipe member for an intake and exhaust system of an internal combustion engine in which gas flows according to an operation of the internal combustion engine. The further installation structure is provided with a pressure introducing pipe having a pressure inlet and a pressure outlet, which is connected on a side of the pressure inlet to the pipe member and on a side of the pressure outlet to the pressure detecting apparatus so that inner pressure in the pipe member may be introduced to and detected by the pressure detecting apparatus. The pressure introducing pipe has a projecting portion partly protruding an inside of the pipe member to open the pressure inlet toward a downstream of the gas flow and the pressure inlet is formed in a slit shape long narrow along a protruding direction of the projecting portion into the pipe member.
With the structure mentioned above, the invasion of the gas flow into the pressure inlet may be effectively prevented since the pressure inlet is formed in a slit shape long narrow along a protruding direction of the projecting portion into the pipe member.
It is another object of the present invention to provide a pressure detecting apparatus into which dirty material contained in the gas flowing in the intake and exhaust gas system are unlikely to enter.
To achieve the object, in the pressure detecting apparatus to be installed on a pipe member for an intake and exhaust system of an internal combustion engine in which gas flows according to an operation of the internal combustion engine, a pressure introducing pipe has a first and second passages the first passage has a gas entrance and a gas exit on opposite ends thereof, which are opened to an inside of the pipe member, and the second passage is connected at one end thereof to the first passage between the gas entrance and the gas exit and at another end to the pressure detecting apparatus so that a part of the gas flowing in the pipe member bypasses the first passage and flows from the gas entrance to the gas exit due to a pressure difference between the gas entrance and gas exit, while inner pressure in the pipe member may be introduced through the pressure introducing pipe to and detected by the pressure detecting apparatus.
With the apparatus mentioned above, the invasion of the dirty material contained in the gas in the intake and exhaust system into a detecting chamber may be prevented.
It is preferable that the gas entrance is positioned on an upstream side of the gas flow and the gas exit is positioned on a downstream side of the gas flow in the pipe member to obtain a larger pressure difference between the gas entrance and the gas exit.
A gas flow cross sectional area of the first passage is, preferably, larger than that of the second passage. That is, the gas flow cross sectional area of the first passage may be within a range of 5 to 320 mm2 and a total length thereof may be with in a range of 5 to 100 mm, and the gas flow cross sectional area of the second passage may be within a range of 5 to 320 mm2 and a total length thereof may be within a range of 1 to 100 mm.